Retractable utility knife



FIG. 1 is a top plan view of a retractable utility knife showing my new design, shown in the extended condition thereof;

FIG. 2 is a left side elevational view thereof;

FIG. 3 is a bottom plan view thereof;

FIG. 4 is a right side elevational view thereof;

FIG. 5 is a front elevational view thereof; and,

FIG. 6 is a rear elevational view thereof.

The broken lines show portions of the retractable utility knife that form no part of the claimed design. 

I claim the ornamental design for a retractable utility knife, as shown and described. 